Mathematical Modelling of the Radiation Fields from Microwave Primary-Feed Antennas

Numerical modelling of reflector antenna radiation fields has received considerable attention in the literature and techniques based upon Physical-optics are widely employed. A major limitation in the application of such techniques is the accurate mathematical modelling of the primary-feed radiation which is incident upon the reflector or sub-reflector surface. This aspect of the modelling has become increasingly important with the advent of microwave systems demanding high levels of polarisation purity. The paper describes the results of an examination of some mathematical modelling techniques, and provides both theoretical and experimental support for the conclusions drawn. Rectangular and cylindrical smooth-walled waveguide horns and cylindrical corrugated horns are considered in some detail and some insight offered with respect to the factors governing the cross-polarisation characteristics of these devices.